The world around us is made up of countless objects—from the air we breathe and the food we eat to the chairs we sit on and the stars in the sky. All these things, in the language of science, are collectively called Matter. Chapter 1 of the NCERT Science syllabus, Matter in Our Surroundings, lays the foundation for understanding the physical and chemical nature of the substances that compose our universe.
What is Matter?
In a simple definition, Matter is anything that occupies space and has mass. Since ancient times, philosophers have tried to classify matter. Early Indian philosophers proposed that all matter was composed of five basic elements: air, earth, fire, sky, and water, known as the Panchtatva. Modern scientists, however, classify matter based on its physical properties and chemical nature. This chapter focuses primarily on the physical nature of matter.
Physical Nature of Matter
Matter is not a continuous, solid block, but is actually made up of tiny, discrete particles. This is supported by simple observations, such as when you dissolve sugar in water—the sugar particles fit into the spaces between the water particles, showing that matter is particulate.
Characteristics of Particles of Matter
The tiny particles that make up matter exhibit three main characteristics:
- They have space between them: Evidence for this is seen when substances dissolve, such as salt or sugar in water, as their particles slip into the empty spaces between the water molecules.
- They are continuously moving: The movement of these particles is known as Kinetic Energy. This movement is most evident in the phenomenon of diffusion, where the particles of two different types of matter intermix on their own (e.g., the smell of an incense stick spreading throughout a room). The rate of movement increases with temperature.
- They attract each other: There is a force of attraction between the particles. This force keeps the particles together, but its strength varies greatly across different states of matter, dictating many of their properties.
States of Matter
Based on the strength of the force of attraction between particles and the kinetic energy of the particles, matter primarily exists in three states: Solid, Liquid, and Gas.
| Property | Solid State | Liquid State | Gaseous State |
| Shape | Fixed shape | No fixed shape (takes container’s shape) | No fixed shape (takes container’s shape) |
| Volume | Fixed volume | Fixed volume | No fixed volume |
| Compressibility | Negligible | Very low | Highly compressible |
| Fluidity/Rigidity | Rigid (cannot flow) | Fluid (can flow) | Fluid (can flow) |
| Inter-particle Force | Very strong | Less strong | Negligible |
| Kinetic Energy | Least | Intermediate | Highest |
Export to Sheets
Change of State
Matter is not fixed in one state; it can change from one state to another by altering temperature or pressure.
Effect of Change of Temperature
- Melting (Fusion): Solid → Liquid. The temperature at which a solid melts to become a liquid at atmospheric pressure is its melting point. The heat energy supplied during melting without a rise in temperature is called Latent Heat of Fusion.
- Boiling (Vaporization): Liquid → Gas. The temperature at which a liquid starts boiling rapidly at atmospheric pressure is its boiling point. The heat energy supplied during boiling without a rise in temperature is called Latent Heat of Vaporisation.
- Sublimation: Solid → Gas (or vice-versa) directly, without passing through the liquid state (e.g., camphor or dry ice).
Effect of Change of Pressure
Applying pressure and reducing temperature can change a gas into a liquid (liquefaction). For example, Carbon Dioxide gas can be solidified by increasing pressure and lowering temperature; this solid CO2 is known as Dry Ice.
Evaporation: A Surface Phenomenon
Evaporation is the process where a liquid changes into a vapour at any temperature below its boiling point. It is a surface phenomenon, meaning only the particles at the surface gain enough energy to overcome the forces of attraction and escape as vapour.
Factors Affecting Evaporation
The rate of evaporation increases with:
- Increase in Surface Area: (e.g., clothes dry faster when spread out).
- Increase in Temperature: (e.g., water evaporates faster on a hot day).
- Decrease in Humidity: (less water vapour in the air allows for more evaporation).
- Increase in Wind Speed: (fast wind carries away water vapour, decreasing the humidity of the surroundings).
Evaporation Causes Cooling
During evaporation, liquid particles absorb energy from the surroundings to compensate for the energy lost during their change into vapour. This absorption of energy from the surroundings makes the surroundings cooler. This is why sprinkling water on the roof on a hot day, or using a desert cooler, provides a cooling effect.
